1. Field of the Invention
The present invention relates to a stator core for an AC generator to be mounted on a vehicle and a production process therefor.
2. Description of the Prior Art
FIG. 7 is a sectional view of a car AC generator of the prior art. This AC generator comprises a case 3 formed by connecting an aluminum front bracket 1 and an aluminum rear bracket 2 by a bolt 3B, a shaft 5 provided in the case 3 and fitted with a pulley 4 for receiving the torque of an engine transmitted from a belt at one end, a random type rotor 6 fixed to the shaft 5, fans 6F fixed to both sides of the rotor 6, a stator 7A fixed on the inner wall of the case 3, slip rings 8, fixed to the other end of the shaft 5, for supplying a current to the rotor 6, a pair of brushes 9 and 9 which slide in contact with the slip rings 8, a brush holder 10 for storing the brushes 9 and 9, a rectifier 11, electrically connected to the stator 7A, for rectifying an AC generated in the stator 7A into a DC, a heat sink 12 attached to the brush holder 10, and a regulator 13, attached to the heat sink 12, for regulating an AC voltage generated in the stator 7A. Denoted by 14a and 14b are bearings, and 15 brackets for connecting the AC generator to the engine.
The above rotor 6 comprises a rotor coil 6A for generating a magnetic flux with a current supplied and a pole core 6B for covering the rotor coil 6A and forming a magnetic pole with the magnetic flux. The pole core 6B consists of a pair of pole core unit 6x and a pole core unit 6y which engage with each other. The pole core units 6x and 6y are made from iron and have claw-like magnetic poles 62 and 62, respectively.
The stator 7A comprises a stator core 17A and a stator coil 17B formed of a conductor wound round the stator core 17A. An AC is generated in the stator coil 17B by the rotation of the rotor 6 according to changes in the magnetic flux from the rotor coil 6A.
In the car AC generator constituted above, a current is supplied to the rotor coil 6A from a battery (unshown) through the brushes 9 and 9 and the slip rings 8 to generate a magnetic flux. Meanwhile, the pulley 4 is driven by the engine and the rotor 6 is turned by the shaft 5, thereby giving a rotating field to the stator coil 17B to generate electromotive force in the stator coil 17B. This AC electromotive force is rectified into a DC by the diodes 16 and 16 of the rectifier 11, the DC is regulated by the regulator 13, and the regulated DC is charged into the battery.
FIG. 8 is a sectional view of a car brushless AC generator of the prior art. The same or corresponding elements as those of FIG. 7 are given the same reference symbols and their descriptions are omitted. In the case of this car brushless AC generator, when the engine is started, an excitation current is supplied from the battery to an excitation coil incorporated in an excitation core 19 through a regulator 13A and the pole core units 6x and 6y of the rotor 6 are turned by the rotation of the shaft 5, whereby electromotive force is generated in the stator coil 17B of the stator 7A. This AC electromotive force is rectified into a DC by the diodes 16 and 16 of the rectifier 11, the DC is regulated by the regulator 13A, and the regulated DC is charged into the battery.
FIG. 9 is a schematic perspective view showing an example of stator core 17A used in the car AC generator of the prior art shown in FIG. 7 and FIG. 8. The stator core 17A having a predetermined thickness S in a lamination direction is constructed by winding a single long iron metal sheet 17a which is punched as shown in FIG. 10 spirally in such a manner that the metal sheet layer are placed one upon another to form a cylinder and welding the cylinder at several locations on the peripheral side of the cylinder in the lamination direction. The metal sheet 17a has recesses 17b for forming slots 20 and recesses 17c for forming bolt shelter grooves 21 after lamination. FIG. 11 is a schematic plan view of the stator core 17A.
In FIG. 9, four welding spots are provided on the peripheral side at intervals of about 90.degree. on the basis of the center of the cylinder. Generally speaking, four welding spots are provided from the view point of the strength of the core assembly. Welding is carried out linearly from the upper end to the lower end of the peripheral side of the cylinder with a jig movable in the lamination direction of the cylinder after the cylinder is sandwiched between chucks to bring the layers of the metal sheet 17a into close contact with one another.
A first-phase coil, a second-phase coil and a third-phase coil are inserted into the respective slots 20 of the stator core 17A shown in FIG. 9 to construct the stator 7A shown in FIG. 12 for inducing a three-phase AC. The coil of each phase is inserted into every three slots. Conductors 17e forming the coil are fixed in each slot 20 with varnish 22 as shown in FIG. 13 and the opening side of the slot 20 is sealed with a resin 23.
By winding the long metal sheet 17a punched as shown in FIG. 10 spirally in such a matter that the metal sheet layers are placed one upon another, a plurality of bolt shelter grooves 21 are formed linearly on the peripheral side of the stator core 17A so that they are continuous in a vertical direction and parallel to the lamination direction of the metal sheet 17a. The bolt shelter grooves 21 are formed at intervals of 10.degree., for example, on the basis of the center of the stator core 17A.
Besides the above method, the stator core having a predetermined thickness may be constructed by placing a plurality of ring-shaped metal sheets one upon another to form a cylinder and welding the peripheral side of the cylinder at several locations in the same manner as described above.